Crimpable fibres of acrylonitrile/nu-methylol acrylamide copolymers



United States Patent 3,399 177 CRIMPABLE FIBRES Oli ACRYLONITRlLE/N-METHYLOL ACRYLAMIDE COPOLYMERS Frank Reeder and James Dennis Grifliths,Coventry, England, assignors to Courtaulds Limited, London, England, aBritish company No Drawing. Filed June 9, 1964, Ser. No. 373,876 Claimspriority, application Great Britain, June 13, 1963, 23,572/63 4 Claims.(Cl. 260-855) This invention is concerned with inherently crimped orcrimpable fibres in the form of staple fibres, continuous filaments,spun yarns or continuous filament threads and extends to knitted andwoven goods incorporating such fibres.

It has been proposed to make crimpable polyacrylonitrile fibres byimposing an asymmetric cross-section on the fibres. According to oneproposal, a fibre is composed of two chemically different polymers whichoccupy discrete collateral zones. The fibres are made by spinning thepolymers side by side through each hole of a spinning jet. The polymersrespond diflierently to heat, one shrinking more than the other, so thatwhen the fibre is heated, it is drawn into a helical coil in which themore shrunken polymer follows the shorter path on the inside of thecoil.

In a second process, a chemically homogeneous copolymer is extrudedthrough an asymmetric jet hole in which the polymer is subjected todifferent amounts of shear across the hole. The extruded polymer isimmediately coagulated to form a fibre which retains substantially theshape imposed by the jet-hole, and is stretched and dried under tension.The structure of this fibre is asymmetric in the physical properties ofthe polymer; that part of the polymer which was most highly shearedduring extrusion is the most highly orientated and strained part of thefibre and, therefore, the part which shrinks most when the fibre isheated. This fibre, too, assumes a helically coiled configuration whenit is heated.

The essence of both processes is the mechanical impo' sition of achemical or physical asymmetry on the fibre. It is surprising,therefore, to find a process for making inherently crimped or crimpablefibres which does not rely on imposing asymmetry on the fibresmechanically.

A crimped or crimpable fibre according to the present invention is afibre of a copolymer containing a major proportion of acrylonitrile andfrom 7 to 20 mol percent of an N-methylol or a latent N-methylolderivative of an ethylenically unsaturated acid amide.

Wet-spun fibres which are stretched wet and dried under little or notension, crimp spontaneously during drying, whilst those which arestretched-strained by being dried under tension or stretched afterdrying, crimp when heated to above their second order transitiontemperature.

The amide derivative is preferably derived from acrylamide ormethacrylamide. N-methylol acrylamide and N- methylol methacrylamide areexamples of the derivatives comprising free methylol groups, but weprefer the latent N-methylol derivatives in which the hydrogen of thehydroxyl groups of the N-methylol group is replaced by an alkylincluding a hydroxy alkyl group, or a secondary amino group, N(R) whereR is alkyl, to reduce the chemical activity of the substance at nearambient temperatures, and increase the stability of the polymer duringthe stages of manufacture and spinning into fibres. The latentN-methylol derivatives must, however, be capable of interacting to crosslink the polymer or of generating N-methylol groups which interact tocause cross linking at temperatures above those encountered in earlierprocess steps i.e. above about 100 C. The preferred, latent N-methylolderivatives are N (methoxy methyl) acrylamide and N (ethoxy methyl)acrylamide and the analogous derivatives of methacrylamide.

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The fibre may be made using wetor dry-spinning techniques, although awet-spinning process is preferable, particularly one in which a solutionof the polymer in concentrated sodium thiocyanate solution is extrudedinto water or dilute sodium thiocyanate solution to form fibres whichare stretched by at least 500 percent in hot water or steam. The fibresmay then be dried under tension to induce the stretch-strainedcharacter, or, after having been dried when relaxed the fibres may bestrained by being stretched again. The stretched-strained fibres developcrimp, on being heated, preferably in contact with water or steam, toabove their second order transition point which in all cases is lessthan 100 C.

The spinning process can be made to yield crimped fibres directly if thenever-dried fibres are dried under little or no tension.

The polymer solution is homogeneous and may be extruded through circularjet holes so that no asymmetry is imposed mechanically on the fibre.

At the present time there is no completely acceptable theory to accountfor the ability of the fibres to crimp. It is equally surprising thatsome fibres have non-circular cross-sections. Fibres made by a wetspinning process from a copolymer having more than 10 percent of N-methylol acrylamide, for example, were found to have a ribbon-like shapein which the width is 5 or 6 times the thickness and the cross-sectionis fiat or curled on itself to a C-shape. It will be understood,however, that the non-circular shape is not an inevitable feature of thefibres of this invention and that some circular cross-sectioned fibreshave been made with the ability to crimp.

The fibres of this invention are remarkable also for their ability toshrink when heated. Shrinkages of more than 40 percent and frequently ashigh as percent have been observed.

The simultaneous shrinking and crimping which the fibres show whenheated to above C. has a number of useful applications, amongst whichare (i) the formation of a bulkier thread of crimped continuousfilaments by the application of heat,

(ii) the formation of a bulkier spun yarn in which the fibres are thoseof this invention alone or in blend with other and preferably moreheat-stable fibres,

(iii) shrinking and bulking a woven or knitted fabric in the piece ormade up into oversized garments.

The crimp can be eliminated from fibres which have been heated only longenough to develop the crimp, merely by stretching. However, it ispossible to set the crimp in the fibres by cross-linking and the polymerrequires no added reactant in order to do this. The N- methylol amidegroups or latent N-methylol amide groups may be condensedintermolecularly to form methylene or dimethylene ether bridges. Thecondensation is catalysed by acids and some salts, for example thosedisclosed as catalysts for the reaction of cellulose and formaldehyde inBritish patent specification No. 930,132. In a preferred polymer, anacidic monomer, for example methallyl sulphonic acid, is incorporated toact as a catalyst for the cross-linking reaction. The cross-linkingreaction requires that the fibre incorporating or impregnated with acatalyst is heated and, as heat is also required to develop the crimp,it is possible to combine both steps in a single treatment, particularlyas the rate of crimping is so much more rapid than that of condensationreaction, that virtually all the cross-links are formed in the alreadycrimped fibre.

Once the polymer is cross-linked, the crimp proves remarkably stable andis retained or regained during repeated cycles of washing and drying andcycles of tensioning and relaxing.

The invention is illustrated by the following examples in which partsare by weight.

3 Example 1 'A' polymerisation chargewas made up of:

Parts Acrylonitrile 315 N-methylol acrylamide 107 Azobisisobutyronitrile3.9 Iso-propanol 47 Sodium thiocyanate crystals 1955 Water 572 and thepH adjusted to 8. The charge was fed to a tubular reactor and thereheated to a temperature of 80 C. The average dwell time of the charge inthe reactor was 1 /2 hours. The charge emerged as a homogeneous, pale,viscous copolymer solution. Analysis showed that 92 percent of theacrylonitrile and N-methylol acrylamide had copolymerised and that thecopolymer had an intrinsic viscosity of 1.31.

The copolymer solution. was extruded through a 20 hole jet, each holehaving a diameter of 0.005 inch into a water bath at ambient temperatureto form fibres. The fibres were stretched by 20 times in live steam,collected on a bobbin and dried. The fibres had an average denier of4.4. The stretching step was modified after the collection of the firstsample, to stretching the fibres in water at 87 C. by 12% times.

The fibres from both stretching operations crimped instantaneously whenrelaxed in contact with a surface at 120 C.

The fibres were cross-linked by first impregnating them with a 5 percentMgCl solution and finally heating them at 160 C. for 2 hours. When thefibres were relaxed and heated, the crimp was set by the cross-linkingto the extent that it could not be removed by straining the fibres. Thecross-linked fibres were also, insoluble in a wide variety of liquids,some of which were excellent solvents for the copolymer beforecross-linking.

Example 2 A mixture was formed of:

Parts Thiourea dioxide 2.1 N-methoxy methyl acrylamide 14.15 Acrylamide8.85 NaCN S 450 Water 302 Isopropanol 3 1 Acrylonitrile 1 17Azoisobutyronitrile 1.4

The pH of the solution was adjusted to 6 with a sodium hydroxidesolution and more water was added to bring the mixture to a total of1,000 parts.

Half the mixture was placed in a stirred reactor equipped with a refluxcondenser and the temperature of the mixture was raised to 80 C. After10 minutes, the addition of the remainder of the mixture to the reactorwas started and continued at a constant rate over another hour. Heatingand stirring were continued for a further 80 minutes, after whichunreacted acrylonitrile was removed under vacuum, leaving a clear, paleyellow, viscous solution.

The conversion of monomer to polymer was found to be 92 percent completeand the inherent viscosity of the polymer (in 50 percent w./w. aqueousNaCNS was 0.90.

The viscous solution was extruded through a 20 hole jet, each holehaving a diameter of 0.005 inch, into water at 4 C. to form filamentswhich were taken up at 2.5 m./m., stretched ten times in steam andcollected. The still-wet filaments were subsequently washed with water,impregnated with an 11 percent solution of H PO in water and allowed todry in air in a relaxed condition. The dry filaments were stronglycrimped and possessed an asymmetric cross-section. At this stage thefilaments could be dissolved in a 50 percent w./w. aqueous NaCNSsolution and the crimp could be removed by tensioning the filaments inlive steam. owever, after the filaments were cured in a relaxedcondition'by heating to 150 C. for 4 minutes, the fibre was onlyslightly swollen by the 50 percent NaCNS solution and the crimp couldnot be pulled out in steam. The cured fibre had a tenacity of 1.7 gramsper denier and an extensibility of 28 percent.

When the freshly-spun fibres were dried under tension they did notdevelop crimp, but could be made to do so on heating to say 160 C. in arelaxed state at which-temperature the filaments may also be cured. Suchfilaments had a tenacity of 3.12 grams per denier and an extensibilityof 13.7 percent.

Example 3 A polymerisation process and extrusion identical with thosedescribed in Example 2, with the exception that the freshly-extrudedfilaments were stretched by only 5 times in water at 70 0., providedfilaments which developed more crimp on air-drying in a relaxedcondition.

When the spinning process was altered so that the freshly extrudedfilaments were stretched by 24 times in steam and the filaments werecured in a relaxed state, the filaments acquired a tenacity of 3.28grams per denier and an extensibility of 24 percent.

Example 4 The polymerisation procedure of Example 2 was followed with amixture having a pH of 6 and composed of:

Parts Acrylonitrile 122 N-methylol acrylamide 29.2 Thiourea dioxide 2.27Azoisobutyronitrile 1.51 Isopropanol 31 NaCNS 450 Water to make up atotal of 1000 The inherent viscosity of the polymer was 0.87 asdetermined in 50 percent NaCNS.

The extrusion was similar to that described in Example 2 with theexception that the freshly-extruded filaments were stretched by 26times, soaked in a 1 percent aqueous solution of NH Cl, before drying ina relaxed condition in air. The dried fibre was highly crimped and couldbe cured by heating for 4 minutes at 150 C.

Example 5 The polymerisation process disclosed in Example 2 was used topolymerise the monomers in a charge made up of:

The resultant viscous solution was extruded through a 40 hole jet, eachhole of 0.003 inch diameter, into water at 30 C. The filaments weretaken up at 2.5 m./m., stretched 15 times in water at C., washed indilute sulphuric acid and dried in a relaxed state at C. The filamentcrimped during the last step, but not to the extent of the filament madeby following the procedure of Example 2. At this stage the filament hada tenacity of 1.07 and an extensibility of 43 percent. After curing for8 minutes at C., the filament had a tenacity of 1.72, an extensibilityof 34 percent and an imbibition in 50 percent NaCNS of 23 percent.

Example 6 The polymerisation process of Example 2 was followed inpreparing a solution of a copolymer of 95 parts of acrylonitrile and 15parts of N-methylol-acrylamide. The solution was extruded into Water at12 C. to form filaments of circular cross-section which crimpedspontaneously when dried relaxed. The filaments formed by extruding thesolution into water at 4 C. did not crimp spontaneously.

What We claim is:

1. A chemically and physically homogeneous, inherently crimpable fiberof a copolymer consisting essentially of a major proportion ofacrylonitrile and from 7 to 20 mol percent of an N-substitutedderivative of acylamide or methacrylamide, said derivative being chosenfrom the group consisting of derivatives having N-methylol groups andderivatives capable of forming N-methylol groups on heating to aboveabout 100 C., said copolymer being formed by free-radicalcopolymerization.

2. A fibre as claimed in claim 1 in a stretch-strained condition.

3. A fibre as claimed in claim 1 in which the latent N-rnethylolderivative is chosen from the group consisting of N(methoxymethyl)acrylamide, N(ethoxymethyl) rnethacrylamide and N(butoxy methyl)acrylamide.

4. A fibre as claimed in claim 1, incorporating at least 10 percent ofthe N-substituted amide and having a ribbon-like shape.

References Cited UNITED STATES PATENTS 2,560,680 7/ 1951 Allewelt260-855 2,649,438 8/1953 Bruson 260-855 2,796,656 6/1957 Schappel et a1.161-173 2,931,091 4/1960 Breen 161-173 3,016,283 1/1962 Schappel 2641683,065,042 11/1962 Bradley 264-168 2,718,515 9/ 1955 Thomas 260-8552,761,856 9/1956 Suen et a1 260- 855 2,984,588 5/1961 Graulick et al.26085.5

FOREIGN PATENTS 1,382,682 11/1964 France.

643,834 6/ 1964 Belgium.

JOSEPH L. SCHOFER, Primary Examiner. HARRY WONG, Assistant Examiner.

1. A CHEMICALLY AND PHYSICALLY HOMOGENEOUS, INHERENTLY CRIMPABLE FIBEROF A COPOLYMER CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OFACRYLONITRILE AND FROM 7 TO 20 MOL PERCENT OF AN N-SUBSTITUTEDDERIVATIVE OF ACYLAMIDE OR METHACRYLAMIDE, SAID DERIVATIVE BEING CHOSENFROM THE GROUP CONSISTING OF DERIVATIVES HAVING N-METHYLOL GROUPS ANDDERIVATIVES CAPABLE OF FORMING N-METHYLOL GROUPS ON HEATING TO ABOVEABOUT 100*C., SAID COPOLYMER BEING FORMED BY FREE-RADICALCOPOLYMERIZATION.